How Many PCIe 4.0 x4 SSDs Can I Add While Keeping My GPU at x16 with a 9950X3D and X870E Motherboard?

If you're aiming for maximum PCIe 4 x4 ports, you could prioritize a motherboard designed for that and ditch any unnecessary SATA connections. With an ideal setup, you could have one SSD connected to the CPU, two to the first chipset, and three to the second chipset—totaling six—especially if you opt for an X670/X670E board to gain an extra slot since USB4 would be non-mandatory.

The X870E designation doesn't tell the whole story since different manufacturers use that chipset for different boards. You'll need to check the specs of the specific motherboard you're interested in.

It varies based on the motherboard and how it manages lane sharing. For example, the MSI X870E Edge TI WIFI supports four M.2 drives at full speed while still allowing the GPU to run at x16, but you'd need to disable USB 4 since one of the M.2 slots shares lanes with it.

Absolutely, it’s all about the motherboard model. Take the MSI Tomahawk X870E, for instance; it has lane sharing with a high-speed USB-C port. Update: MSI is rolling out their new X870E MAX boards that won't have lane sharing, letting all M.2 slots run without performance slowdown.

It really depends on the model of your motherboard. Some have more M.2 slots available than others. If maximizing SSDs is your priority, I can suggest a few good models that might fit your needs.